The present invention relates to an electrostatic recording material using a sheet of multi-layered synthetic paper as a support. More particularly, the present invention relates to an electrostatic recording material that employs a sheet of multi-layered synthetic paper as a support suitable for use in electrostatic recording wherein the surface layer of said paper is formed of a clear film layer that is substantially free of any inorganic fine powder.
Electrostatic recording materials wherein the support is formed of a multi-layered sheet of synthetic paper containing 8-65 wt % of an inorganic fine powder in the outermost layer in contact with the electroconductive layer [as described in Japanese Patent Publication No. 40794/1971 (corresponding U.S. Pat. No. 4,318,950) and Japanese Patent Publication Laid-Open No. 141339/1981] are known to have better dimensional stability, water resistance and tensile strength as compared with electrostatic recording materials using pulp paper as the support. They are also superior to electrostatic recording materials which are supported on a clear polyester film that is free from any inorganic fine powder in that they have better adhesion between the support and the electroconductive layer and that they accept writing with a pencil. However, in order to provide improved printing properties, the synthetic paper containing 8-65 wt % of an inorganic fine powder in the outermost layer in contact with the electroconductive layer has inorganic fine particles projected outwardly from the surface. Some of these inorganic particles provide projections or elevations that exceed the general requirements for the surface of electrostatic recording materials and the surface of the support having such elevations is not suitable for use in electrostatic recording materials. For the asperity of the surface, or the gap between the dielectric layer and the charging electrode, that is required for providing satisfactory printed images, Japanese Patent Publication No. 18307/1966 (corresponding to U.S. Pat. No. 3,354,464) teaches the range of 2-20 .mu.m, and Japanese Patent Publication No. 8204/1957 (corresponding to U.S. Pat. No. 2,825,814) teaches the range not exceeding about 10 .mu.m, preferably between 2 and 5 .mu.m. Japanese Patent Publication No. 33703/1981 (corresponding to U.S. Pat. No. 3,657,005 and 3,711,859) discloses a spacer means that projects a distance of 1.27-10.16 .mu.m from the outer surface of the dielectric layer. As shown in these patents, if the height of the spacer projecting from the surface of an electrostatic recording material is excessive, too much difficulty is involved in applying pulsive voltage to perform satisfactory printing. Trouble also arises from the separation (dropping out) of the inorganic fine particles, and solid printed areas in an electrostatic recording material that employs a conventional sheet of synthetic paper as the support contain no less than 50 white spots per 0.1 m.sup.2 which are no smaller than 1 mm in diameter.